This invention relates to new nonionic cellulose ethers with improved thickening effects, especially in paint compositions. The improvements depend on the presence of hydrophobic substituents having a poly(oxyethylene) spacer between a large aliphatic group and the linkage to the cellulose ether.
U.S. Pat. No. 4,228,277 discloses associative water-soluble nonionic cellulose ethers of the so called associative type. They contain as a modifying substituent a C10 to C24 long chain alkyl group which may be introduced by reacting a water-soluble cellulose ether and a suitable amount of the corresponding C10 to C24 epoxide.
In EP-A-390 240 associative nonionic cellulose ethers are described which may contain hydrophobic substituents of the formula 
where R is a hydrophobic group containing 8-36 carbon atoms, A is an alkylenoxy group having 2-3 carbon atoms and n is a number from 0 to 6. In Example F the publication discloses an ethyl hydroxyethyl cellulose ether containing the hydrophobic substituent 
The degree of substitution of this group is 0.016.
It has now been found that the properties of the prior art nonionic cellulose ethers can be improved by the present nonionic cellulose ethers which have improved thickening effects, especially in paint compositions.
The present invention generally relates to nonionic cellulose ethers having improved thickening effects compared to the prior art. The improvements depend on the presence of hydrophobic substituents having a poly(oxyethylene) spacer between a large aliphatic group and the linkage to the cellulose ether. The invention also relates to a thickener which comprises the nonionic cellulose ethers of the present invention.
The present invention generally relates to nonionic cellulose ethers having improved thickening effects compared to the prior art. The properties of the present nonionic cellulose ethers are improved by introducing into the nonionic cellulose ether a hydrophobic modifying group of the general formula 
where R is an aliphatic group of 12-22 carbon atoms and n is a number from 3 to 7 with a degree of substitution of 0.003-0.102. The hydrophobically modified cellulose ether may have a viscosity of 20-15000 mPaxc2x7s, preferably 100-12000 mPaxc2x7s, and more preferably 150-4000 mPaxc2x7s, measured in a 1% by weight water solution with a StressTech rheometer from Rheologica, equipped with a 4 cm 1xc2x0 cone and plate system, at 20xc2x0 C. + or xe2x88x92 0.1xc2x0 C. The rheometer was put in the constant shear mode and all viscosities were measured at the Newtonian plateau, characterized by a shear rate independent viscosity.
Extensive studies have shown that the length of the spacer, that is to say the length of the hydrophilic group (xe2x80x94C2H4Oxe2x80x94)n positively affects the thickening, levelling and high shear viscosity in paint compositions. For example, the contribution of the thickening effect of the group 
is higher than the effect of the group 
Very surprising is also the fact that the thickening effect of the long spacer is more pronounced the larger the aliphatic group is. Preferably R is an aliphatic group of 14-20 carbon atoms and n is a number from 3 to 5. Even if larger aliphatic groups and higher values of n will further improve the viscosity, such high viscosities will normally not be required.
Besides the hydrophobic group the cellulose ether may contain lower alkyl substituents such as methyl, ethyl or propyl, or hydroxyalkyl substituents as hydroxyethyl, hydroxypropyl or hydroxybutyl or combinations thereof. The substituent and the degree of substitution are chosen so that the associative cellulose ethers of the invention become water-soluble or water-dispersable.
It has also been found that cellulose ethers, substituted with a group of the formula I and having a low degree of polymerisation, have remarkably favourable properties. These cellulose ethers have a unique combination of high associative thickening effect, high hydrophilicity and comparatively low thickening effect depending on the length of the cellulose chain. The unique combination of properties depends on the fact that the hydrophilicity of the large spacer of the group I increases the hydrophilicity of the cellulose ether and at the same time the associative thickening effect of the group I. The unique properties of these cellulose ethers can for example be utilized to improve the levelling, sagging and spatter of paint compositions.
The differences in DP between cellulose ethers may easily be measured by determining the DP viscosity in a blend of diethylene glycol monobutylether and water in a weight ratio of 20:80. In such a blend all hydrophobic associations are broken and the viscosity depends on the length of the cellulose chain. In this context the DP viscosity means the viscosity of 1% by weight of cellulose ether dissolved in the blend divided by 2.7. The DP viscosity value indicates an average DP value of the cellulose ether. According to the invention the cellulose ethers normally have a DP viscosity of 15-200 mPaxc2x7s. In paint compositions the DP viscosity of the cellulose ethers are preferably 20-100 mPaxc2x7s.
The cellulose ethers of the invention may be prepared by using known process steps. For example an alkali cellulose and suitable reactants can be reacted in the presence of an alkaline catalyst in order to introduce low alkyl groups and/or hydroxyalkyl groups in such amounts that the intermediate cellulose ethers obtained are water soluble. This intermediate cellulose ether product and a reactant having the formula 
in which R and n have the meaning mentioned above, at elevated temperature and in the presence of an alkaline catalyst, to form a cellulose ether according to the invention.
Suitable water-soluble ethers to which the hydrophobic group is added include, but are not limited to alkyl cellulose, alkyl hydroxyalkyl cellulose and hydroxyalkyl cellulose. Specific examples of such cellulose ethers include methyl hydroxyethyl cellulose, methyl hydroxypropyl cellulose, hydroxyethyl cellulose, methyl cellulose, hydroxyethyl hydroxypropyl cellulose, ethyl hydroxyethyl cellulose, methyl ethyl hydroxyethyl cellulose and methyl hydroxyethyl hydroxypropyl cellulose. Preferred cellulose ethers are alkyl hydroxyalkyl celluloses, such as methyl hydroxyethyl cellulose, methyl ethyl hydroxyethyl cellulose and ethyl hydroxyethyl cellulose; and hydroxyethyl cellulose.
The hydrophobically modified cellulose ethers of the invention may advantageously be used as a colloid stabilizer, thickener or reology modifier. Typical application areas are aqueous paint formulations, such as latex paints; cosmetics, such as shampoos and conditioners; detergent compositions, such as surface cleaners and compositions for laundry; and paper coating compositions.
The cellulose ethers may advantageously be used in water-based flat, semi-flat and semi-gloss paints. The amounts added of the cellulose ethers vary depending on both the composition of the paints and the substitution and viscosity of the cellulose ethers, but normally the addition is 0.2-1% by weight of the paints. Suitable binders are emulsion binders, such as alkyd resins, and latex binders, such as polyvinyl acetate, copolymers of vinyl acetate and acrylate, copolymers of vinyl acetate and ethylene, copolymers of vinyl acetate, ethylene and vinyl chloride and copolymers of styrene and acrylate. The latex binders are often stabilized with anionic surfactants.
The present cellulose ethers are much more versatile thickeners than earlier known associative nonionic cellulose ethers. The paint formulator has the possibility to affect the final paint properties to a very high extent. The present cellulose ethers can be used in all types of paints ranging from low to high PVC, and for interior as well as exterior use. They contribute to the following paint properties:
low spatter
good film build
good flow and levelling
low sag
The present invention and the advantages of the present cellulose ethers are further illustrated by the following examples.